Higgins and Pickering show up the next day at Mrs. Higgins' home in a state of distraction because Eliza has run away. They are interrupted by Alfred Doolittle, who enters resplendently dressed, as if he were the bridegroom of a very fashionable wedding. He has come to take issue with Henry Higgins for destroying his happiness. It turns out that Higgins wrote a letter to a millionaire jokingly recommending Doolittle as a most original moralist, so that in his will the millionaire left Doolittle a share in his trust, amounting to three thousand pounds a year, provided that he lecture for the Wannafeller Moral Reform World League. Newfound wealth has only brought him more pain than pleasure, as long lost relatives emerge from the woodwork asking to be fed, not to mention that he is now no longer free to behave in his casual, slovenly, dustman ways. He has been damned by "middle class morality." The talk degenerates into a squabble over who owns Eliza, Higgins or her father (Higgins did give the latter five pounds for her after all). To stop them, Mrs. Higgins sends for Eliza, who has been upstairs all along. But first she tells Doolittle to step out on the balcony so that the she will not be shocked by the story of his new fortune.
When she enters, Eliza takes care to behave very civilly. Pickering tells her she must not think of herself as an experiment, and she expresses her gratitude to him. She says that even though Higgins was the one who trained the flower girl to become a duchess, Pickering always treated her like a duchess, even when she was a flower girl. His treatment of her taught her not phonetics, but self-respect. Higgins is speaking incorrigibly harshly to her when her father reappears, surprising her badly. He tells her that he is all dressed up because he is on his way to get married to his woman. Pickering and Mrs. Higgins are asked to come along. Higgins and Eliza are finally left alone while the rest go off to get ready.
They proceed to quarrel. Higgins claims that while he may treat her badly, he is at least fair in that he has never treated anyone else differently. He tells her she should come back with him just for the fun of it--he will adopt her as a daughter, or she can marry Pickering. She swings around and cries that she won't even marry Higgins if he asks. She mentions that Freddy has been writing her love letters, but Higgins immediately dismisses him as a fool. She says that she will marry Freddy, and that the two will support themselves by taking Higgins' phonetic methods to his chief rival. Higgins is outraged but cannot help wondering at her character--he finds this defiance much more appealing than the submissiveness of the slippers-fetcher. Mrs. Higgins comes in to tell Eliza it is time to leave. As she is about to exit, Higgins tells her offhandedly to fetch him some gloves, ties, ham, and cheese while she is out. She replies ambivalently and departs; we do not know if she will follow his orders. The play ends with Higgins's roaring laughter as he says to his mother, "She's going to marry Freddy. Ha ha! Freddy! Freddy!! Ha ha ha ha ha!!!!!"
This final act brings together many of the themes that we have examined in the other acts, such as what constitutes the determinants of social standing, the fault of taking people too literally, or for granted, the emptiness of higher English society, etc. With regard to the first of these themes, Eliza makes the impressively astute observation that "the difference between a lady and a flower girl is not how she behaves, but how she's treated." The line packs double meaning by stating clearly that what is needed is not just one's affectation of nobility, while her delivery is proof of the statement itself as she has grown enough to make such an intelligent claim. Quite contrary to the dresses, the vowels, the consonants, the jewelry (significantly, only hired) that she learned to put on, probably the greatest thing she has gained from this experience is the self-respect that Pickering endowed her with from the first time he called her "Miss Doolittle." In contrast to the "self-respect" that Eliza has learned is the "respectability" that Doolittle and his woman have gained, a respectability that has "broke all the spirit out of her." While respectability can be learned, and is what Higgins has taught Eliza, self-respect is something far more authentic, and helps rather than hinders the growth of an independent spirit. Alfred Doolittle makes the unmitigated claim that acquiring the wealth to enter this society has "ruined me. Destroyed my happiness. Tied me up and delivered me into the hands of middle class morality." Higgins' haughty proclamation--"You will jolly soon see whether she has an idea that I haven't put into her head or a word that I haven't put into her mouth."--mistakes the external for the internal, and betrays too much unfounded pride, which is the ultimate cause of his misunderstanding with Eliza.
The greatest problem that people have with Pygmalion is its highly ambivalent conclusion, in which the audience is left frustrated if it wants to see the typical consummation of the hero and heroine one expects in a romance--which is what the play advertises itself to be after all. Most people like to believe that Eliza's talk about Freddy and leaving for good is only womanly pride speaking, but that she will ultimately return to Higgins. The first screenplay of the movie, written without Shaw's approval, has Eliza buy Higgins a necktie. In the London premier of the play, Higgins tosses Eliza a bouquet before she departs. A contemporary tour of the play in America had Eliza return to ask, "What size?" Other films of the play either show Higgins pleading with Eliza to stay with him, or Higgins following her to church. Doubtless, everyone wanted to romanticize the play to a degree greater than that which the playwright presented it. All this makes us question why Shaw is so insistent and abrupt in his conclusion.
However, in an epilogue that Shaw wrote after too many directors tried to adapt the conclusion into something more romantic, he writes, "The rest of the story need not be shewn in action, and indeed, would hardly need telling if our imaginations were not so enfeebled by their lazy dependence on the ready-mades and reach-me-downs of the ragshop in which Romance keeps its stock of 'happy endings to misfit all stories." He goes on to deliver a detailed and considered argument for why Higgins would never marry Eliza, and vice versa. For one, Higgins has too much admiration for his mother to find any other woman even halfway comparable, and even "had Mrs. Higgins died, there would still have been Milton and the Universal Alphabet." To Shaw's mind, if Eliza marries anyone at all, it must be Freddy--"And that is just what Eliza did." The epilogue goes on to give a dreary account of their married life and faltering career as the owners of a flower and vegetable shop (an ironic treatment of the typical "happily ever after" nonsense) in which Freddy and Eliza must take accounting and penmanship classes to really become useful members of society. One can see this whole play as an intentional deconstruction of the genre of Romance, and of the myth of Pygmalion as well.